Places around Raunheim and Hauptbahnof, Frankfurt which i can explore in 4-5 hrs in evening

Evenings are a bit more difficult since things like museums, markets, etc. will be closed. That said, some of the museums in Frankfurt or Mainz may be open later.

These are the towns I go to all the time from Frankfurt as they are easy to get to and are interesting:
Bad Homburg, Kronberg, Königstein, Frankfurt Höchst.
These towns are a bit farther away and may be best for weekends:
Eltville, Limburg, Idstein, Seligenstadt, Büdingen, Gelnhausen, Aschaffenburg, Worms, Marburg, Hessen Park Open Air Museum & the Saalburg near Bad Homburg.

Events in the Rhein Main Region you might enjoy.

• 14-18 Sept. Elsässer Week, Frankfurt Paulsplatz
• 14-18 Sept. Harvest Exhibit, Frankfurt Palmengarten
• 16-20 Sept. Harvest Market, Friedberg
• 17-18 Sept. Fest of Cultures, Offenbach
• 18 Sept. Day of the Cemetery, Frankfurt Hauptfriedhof (English tour 14:30)
• 22-24 Sept. Harvest Fest, Frankfurt Hauptwache & Rossmarkt
• 22-25 Sept. Autumn Market with Sunday Shopping, Wiesbaden
• 23-25 Sept. Gallus Market, Büdingen
• 24-25 Sept. Medieval Fest, Ronneburg Castle Castle Info
• 24 Sept. Soup Fest, Höchst, 12-15:00
• 24-25 Sept. Burg Fest, Rüdesheim
• 24-25 Sept. Medieval Festival, Heidelberg
• 30 Sept.- 9 Oct. Federweisser Fest, Frankfurt Liebfrauenberg
• 1-2 Oct. Kite Festival, Glauburg Celtic World Museum
• 1-3 Oct. Orchid Sale, Frankfurt Palmengarten
• 3 Oct. Antique Market, Frankfurt Konstablerwache
• 3-4 Oct. Harvest Market, Hessen Park Open Air Museum
• 7-10 Oct. Autumn Market, Idstein
• 9 Oct. Harvest Market with Sunday Shopping, Bad Homburg
• 13 Oct. Oktoberfest, Limburg Market Square
• 13-30 Oct. Autumn Flower Show, Frankfurt Palmengarten

Jo beat me to a number of those recommendations. I would add the wonderful old univeristy town of Marburg and the small castle town of Braunfels, but I'm not sure if they are within your time radius via public transportation.

I used to live near Darmstadt and Worms. I didn't love Darmstadt at first glance, but I eventually turned around to it. At first glance, it looks like many of the other cities that were heavily bombed and quickly rebuilt post-war. On closer examination, however, much of the city's German Empire period glory remains, when it was the royal capital of the Grand Duchy of Hessen. A particularly interesting area is the Jugenstil artist colony around the Mathildenhöhe area of the city. The city also hosts a large technical university, so if you're within a few years of college age, you may enjoy the nightlife.

Worms- despite it's very long history, very little remains from before WWII, as it was bombed almost into oblivion. The old cathedral survives, but if you want to see a similar cathedral in a town that was barely hit during the war, go a little further south to it's sister city on the Rhine, Speyer.

Wiesbaden is a beautiful city, as befits its status as one of the richest municipalities in Germany.

Rüdesheim is very touristy and filled with trinket shops, but it has one absolutely unique feature that makes it worth a visit on a weekend night. Many of the restaurants have live Schlager music, and this draws the bachelorette and stag parties from Frankfurt, Wiesbaden and Mainz. The atmosphere becomes quite festive but not too rowdy.

I lived very close to the town of Heppenheim, which I think is worth a quick visit. It has a beautiful market sqaure, overlooked by a castle and vineyards.

Thanks for the list Jo :)
Marked Bad homburg and Kronberg. Königstein seems to be just a castle which i am not sure is open in evening or not. I can't find anything to see in Höchst.
I think Eltville, idstein andSeligenstadt can be done within single evenings, but i will keep them on least priority.
Another one i am adding to the list is Wiesbaden. Not much to see but can be covered easily.

I still got so many weekdays but still cannot figure out places to see.

Tom beat me to Speyer. A very nice place indeed with a very different and pleasing cathedral.

What about week-ends? My suggestions focus on day trips which presumably you could take if you're free on week-ends, and if you are interested especially in war history. If so, then I would suggest doing from Frankfurt days trips to Koblenz, (a number of sites there), Rüdesheim, Wiesbaden, Rastatt (further out near Karlsruhe but still doable), Bad Ems.

Speyer, Koblenz, Rüdesheim, Wiesbaden, Rastatt, Bad Ems - all seems to be too far for evening excursions. On weekends, i plan to visit nearby countries.
It is not that i want to go to some famous tourist attraction. Simple towns near Frankfurt are also fine. I would love to walk around the city in the evening and if not something special, something regular would do the job.